i think you are right, as they appear in my workout records as well.
i think that i was simply not noticing them these days because i had successfully turned the notifications off (as you have) and by doing that it stopped them from giving audible notifications during my workouts (which was the really annoying part of segments).
i also recall that if you do turn on segments you can set their value to a logical number such as 5 km or whatever.
but i think the more intriguing part of this is why it sets such at-first-glance strange (seemingly arbitrary) points for the segment.
i want to think it is looking at my workout map's relevant data (elevation, turn around point, etc) and finding maybe a logical segment length.
i still think that is apple's intention in the case where a user does not override it with his/her own segment length.
here is why i think that apple is trying to figure out a logical segment length based on a variety of inputs:
1. in my own workouts, the segment that apple calculated was remarkably close to my workout's actual point where i was furthest from home and began to turn back towards home. i frequently would rest there for a minute or two (as it was on a hill and the view was very nice). it was uncanny that this location was an apple marked segment. but maybe just coincidental...
2. the following paragraph is from apple's documentation on segments:
(its talking about a specific case for pool swimming)
quote
Because your screen locks during swimming workouts, you can't mark segments. But in Pool Swim workouts, sets are marked automatically every time you rest at the side of the pool for 10 seconds or longer. Auto Sets show up in the workout summary in the Fitness app on your iPhone.
end quote
i think it is trying to identify some logical point/time/elevation/repeated activity point and making that into a segment.
it would make no sense that it is a completely arbitrary data point. its more likely a calculated data point of some sort.